Synopsis: Fixing a Million-Year Clock

A better measure of an iron isotope’s half-life may lead to new ways of dating astrophysical events that unfold over millions of years.
Synopsis figure
A. Wallner et al., Phys. Rev. Lett. (2015)

Radioactive iron-60 (60Fe) is produced at the core of large stars and in supernovae, and it has a half-life of roughly a million years, so its abundance can be used to date astrophysical events on a similar time scale. Scientists have, for example, used the small amount of 60Fe deposited in deep-sea crust to trace the history of supernovae near our Solar System, which may have affected Earth’s climate in the past. But the best measures of 60Fe’s half-life—one performed in 1984, the other in 2009—disagree by nearly a factor of 2. Now, a new experiment settles the discrepancy, enabling more astrophysical studies based on the isotope, such as the monitoring of nucleosynthesis in stars.

To derive the half-life of a long-lived isotope, scientists use samples containing a known number of the nuclei and detect how many of them decay per second. In the case of 60Fe, its decays are monitored by detecting the gamma rays emitted by its daughter nucleus, cobalt-60. But the main uncertainty in earlier experiments has been the initial number of decaying 60Fe nuclei. Working with an iron sample extracted from irradiated copper, Anton Wallner, at the Australian National University, and his colleagues used accelerator mass spectrometry to determine the small concentration of 60Fe isotopes. By comparing this number to the concentration of 55Fe, another rare isotope, they were able to “cancel out” some of the systematic errors that plagued earlier experiments and accurately gauge the 60Fe amount. The half-life they find agrees well with the 2009 value; averaging the two together, Wallner et al. report a value of 2.60 million years and a 2% uncertainty.

This research is published in Physical Review Letters.

–Jessica Thomas


Announcements

More Announcements »

Subject Areas

AstrophysicsNuclear Physics

Previous Synopsis

Plasma Physics

Shocking Pressures

Read More »

Next Synopsis

Electronics

Energetic Flags

Read More »

Related Articles

Synopsis: Gravitational Waves May Hold Dark Matter Secret
Astrophysics

Synopsis: Gravitational Waves May Hold Dark Matter Secret

A theoretical analysis examines the possibility that the black holes detected by LIGO serve as dark matter. Read More »

Synopsis: Cosmic Magnetism Revisited
Cosmology

Synopsis: Cosmic Magnetism Revisited

An analysis of the polarized emission from some 3000 distant radio sources places a stringent upper limit on the strength of the cosmological magnetic field. Read More »

Viewpoint: Black Holes Produce Complexity Fastest
Astrophysics

Viewpoint: Black Holes Produce Complexity Fastest

Theoretical results suggest a precise speed limit on the growth of complexity in quantum gravity, set by fundamental laws and saturated by black holes. Read More »

More Articles